206 lines
7.9 KiB
Rust
206 lines
7.9 KiB
Rust
use crate::utils::paths;
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use crate::utils::{
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is_expn_of, is_type_diagnostic_item, last_path_segment, match_def_path, match_function_call, snippet, snippet_opt,
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span_lint_and_then,
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};
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use if_chain::if_chain;
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use rustc_ast::ast::LitKind;
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use rustc_errors::Applicability;
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use rustc_hir::{Arm, BorrowKind, Expr, ExprKind, MatchSource, PatKind};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use rustc_span::sym;
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declare_clippy_lint! {
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/// **What it does:** Checks for the use of `format!("string literal with no
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/// argument")` and `format!("{}", foo)` where `foo` is a string.
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///
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/// **Why is this bad?** There is no point of doing that. `format!("foo")` can
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/// be replaced by `"foo".to_owned()` if you really need a `String`. The even
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/// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
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/// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
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/// if `foo: &str`.
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///
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/// **Known problems:** None.
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///
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/// **Examples:**
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/// ```rust
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///
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/// // Bad
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/// # let foo = "foo";
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/// format!("{}", foo);
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///
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/// // Good
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/// format!("foo");
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/// ```
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pub USELESS_FORMAT,
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complexity,
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"useless use of `format!`"
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}
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declare_lint_pass!(UselessFormat => [USELESS_FORMAT]);
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impl<'tcx> LateLintPass<'tcx> for UselessFormat {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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let span = match is_expn_of(expr.span, "format") {
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Some(s) if !s.from_expansion() => s,
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_ => return,
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};
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// Operate on the only argument of `alloc::fmt::format`.
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if let Some(sugg) = on_new_v1(cx, expr) {
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span_useless_format(cx, span, "consider using `.to_string()`", sugg);
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} else if let Some(sugg) = on_new_v1_fmt(cx, expr) {
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span_useless_format(cx, span, "consider using `.to_string()`", sugg);
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}
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}
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}
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fn span_useless_format<T: LintContext>(cx: &T, span: Span, help: &str, mut sugg: String) {
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let to_replace = span.source_callsite();
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// The callsite span contains the statement semicolon for some reason.
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let snippet = snippet(cx, to_replace, "..");
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if snippet.ends_with(';') {
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sugg.push(';');
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}
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span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |diag| {
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diag.span_suggestion(
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to_replace,
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help,
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sugg,
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Applicability::MachineApplicable, // snippet
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);
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});
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}
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fn on_argumentv1_new<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) -> Option<String> {
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if_chain! {
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if let ExprKind::AddrOf(BorrowKind::Ref, _, ref format_args) = expr.kind;
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if let ExprKind::Array(ref elems) = arms[0].body.kind;
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if elems.len() == 1;
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if let Some(args) = match_function_call(cx, &elems[0], &paths::FMT_ARGUMENTV1_NEW);
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// matches `core::fmt::Display::fmt`
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if args.len() == 2;
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if let ExprKind::Path(ref qpath) = args[1].kind;
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if let Some(did) = cx.qpath_res(qpath, args[1].hir_id).opt_def_id();
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if match_def_path(cx, did, &paths::DISPLAY_FMT_METHOD);
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// check `(arg0,)` in match block
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if let PatKind::Tuple(ref pats, None) = arms[0].pat.kind;
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if pats.len() == 1;
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then {
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let ty = cx.typeck_results().pat_ty(&pats[0]).peel_refs();
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if *ty.kind() != rustc_middle::ty::Str && !is_type_diagnostic_item(cx, ty, sym::string_type) {
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return None;
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}
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if let ExprKind::Lit(ref lit) = format_args.kind {
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if let LitKind::Str(ref s, _) = lit.node {
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return Some(format!("{:?}.to_string()", s.as_str()));
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}
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} else {
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let snip = snippet(cx, format_args.span, "<arg>");
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if let ExprKind::MethodCall(ref path, _, _, _) = format_args.kind {
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if path.ident.name == sym!(to_string) {
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return Some(format!("{}", snip));
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}
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} else if let ExprKind::Binary(..) = format_args.kind {
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return Some(format!("{}", snip));
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}
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return Some(format!("{}.to_string()", snip));
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}
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}
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}
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None
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}
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fn on_new_v1<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> {
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if_chain! {
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if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1);
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if args.len() == 2;
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// Argument 1 in `new_v1()`
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if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arr) = args[0].kind;
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if let ExprKind::Array(ref pieces) = arr.kind;
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if pieces.len() == 1;
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if let ExprKind::Lit(ref lit) = pieces[0].kind;
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if let LitKind::Str(ref s, _) = lit.node;
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// Argument 2 in `new_v1()`
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if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg1) = args[1].kind;
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if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.kind;
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if arms.len() == 1;
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if let ExprKind::Tup(ref tup) = matchee.kind;
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then {
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// `format!("foo")` expansion contains `match () { () => [], }`
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if tup.is_empty() {
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if let Some(s_src) = snippet_opt(cx, lit.span) {
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// Simulate macro expansion, converting {{ and }} to { and }.
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let s_expand = s_src.replace("{{", "{").replace("}}", "}");
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return Some(format!("{}.to_string()", s_expand))
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}
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} else if s.as_str().is_empty() {
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return on_argumentv1_new(cx, &tup[0], arms);
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}
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}
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}
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None
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}
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fn on_new_v1_fmt<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> {
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if_chain! {
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if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1_FORMATTED);
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if args.len() == 3;
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if check_unformatted(&args[2]);
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// Argument 1 in `new_v1_formatted()`
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if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arr) = args[0].kind;
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if let ExprKind::Array(ref pieces) = arr.kind;
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if pieces.len() == 1;
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if let ExprKind::Lit(ref lit) = pieces[0].kind;
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if let LitKind::Str(..) = lit.node;
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// Argument 2 in `new_v1_formatted()`
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if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg1) = args[1].kind;
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if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.kind;
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if arms.len() == 1;
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if let ExprKind::Tup(ref tup) = matchee.kind;
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then {
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return on_argumentv1_new(cx, &tup[0], arms);
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}
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}
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None
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}
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/// Checks if the expression matches
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/// ```rust,ignore
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/// &[_ {
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/// format: _ {
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/// width: _::Implied,
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/// precision: _::Implied,
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/// ...
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/// },
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/// ...,
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/// }]
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/// ```
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fn check_unformatted(expr: &Expr<'_>) -> bool {
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if_chain! {
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if let ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) = expr.kind;
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if let ExprKind::Array(ref exprs) = expr.kind;
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if exprs.len() == 1;
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// struct `core::fmt::rt::v1::Argument`
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if let ExprKind::Struct(_, ref fields, _) = exprs[0].kind;
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if let Some(format_field) = fields.iter().find(|f| f.ident.name == sym::format);
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// struct `core::fmt::rt::v1::FormatSpec`
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if let ExprKind::Struct(_, ref fields, _) = format_field.expr.kind;
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if let Some(precision_field) = fields.iter().find(|f| f.ident.name == sym::precision);
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if let ExprKind::Path(ref precision_path) = precision_field.expr.kind;
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if last_path_segment(precision_path).ident.name == sym::Implied;
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if let Some(width_field) = fields.iter().find(|f| f.ident.name == sym::width);
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if let ExprKind::Path(ref width_qpath) = width_field.expr.kind;
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if last_path_segment(width_qpath).ident.name == sym::Implied;
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then {
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return true;
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}
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}
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false
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}
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